Two-Stage Laser Could Make Rain, Lightning

A team from the University of Central Florida (UCF) College of Optics & Photonics and the University of Arizona are developing a technique to trigger rain and lightning in clouds with a high-energy laser beam.

The researchers have discovered that surrounding a laser beam with a second beam creates an energy reservoir that can sustain the central beam over long distances. This second “dress” beam helps prevent the dissipation of the primary, higher-intensity beam. Alone, that primary beam breaks down, limiting its reach.

An illustration of a dressed laser filament. Courtesy of UCF College of Optics and Photonics.
“When a laser beam becomes intense enough, it behaves differently than usual — it collapses inward on itself,” said Matthew Mills, a graduate student in the Center for Research and Education in Optics and Lasers (CREOL) at UCF. “The collapse becomes so intense that electrons in the air's oxygen and nitrogen are ripped off, creating plasma — basically a soup of electrons.”

"Because a filament creates excited electrons in its wake as it moves, it artificially seeds the conditions necessary for rain and lightning to occur," Mills said, noting that other researchers have been able to induce electrical events in clouds.

Water condensation and lightning activity in clouds are linked to large amounts of static-charged particles. Stimulating those particles by pointing the proper laser at a cloud could allow scientists to activate rain showers, and potentially even lightning.

Using their new technique, the researchers have demonstrated the ability to control the length of the filament, and were able to extend the laser pulse from 10 inches to about 7 feet.

“Ultimately, you could artificially control the rain and lightning over a large expanse,” Mills said.

The work could lead to “ultra-long, optically-induced filaments or plasma channels that are otherwise impossible to establish under normal conditions,” said Demetrios Christodoulides, a professor at CREOL who assisted with the research. He added that it may become possible for the dressed filaments to spread to distances of hundreds of feet.

Potential applications for the new technique include guiding of microwave signals, as well as long-distance chemical sensors and spectrometers.

The work was funded by a $7.5 million grant from the US Department of Defense. The research is published in Nature Photonics (doi: 10.1038/nphoton.2014.47).

A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.